Conventional painting techniques employ brushing, spraying or rolling paint onto a surface to be coated. In brushing operations, brushes of selected sizes are dipped into containers of paint, part of the paint is removed from the brush by touching a brush or drawing a brush along an edge of the container, the paint-laden brush is touched to the surface to be coated in several places, and then the paint is evenly spread over a limited area before repeating steps of the cycle. Because of the wiping and working nature of brush techniques and the accompanying working of the coating into surface irregularities, brushing has been recognized as one of the desirable ways of producing a coating.
Rolling techniques are accomplished by coating a roller with paint in a tray or a pail, removing part of the paint from the roller, such as by compressing the roller surface on a tray or shaking excess paint from the roller, and rolling the roller along the surface to be painted, usually in one direction and then in another direction. While a normal force is exerted between the roller and the surface to be coated, little frictional forces are developed. Consequently, the paint may not be warped into the surface to be coated as much as in brushing techniques. However, long experience with rolling has indicated that rolling is a desirable method of coating surfaces with paint. In some situations, rolling paint may fling small specks of paint in undesired directions. That condition, while tolerable in some situations, creates problems in other situations.
Spraying techniques employ air operated jet pumps to draw paint from containers and to break up the paint into fine-misted droplets. Paint is propelled by the air from a nozzle to a surface to be coated. Because there is no working of the paint once it reaches the surface, spraying must be less desirable for certain purposes than brushing or rolling techniques. Spraying has the added disadvantage of propelling paint droplets in undesired directions and coating surfaces other than the surface intended to be coated.
While the equipment needed for brushing and rolling may not be cumbersome and expensive, paint spraying apparatus usually requires an air compressor, an air storage device, heavy duty air hose and connection, and an expensive spraying gun. Air compressor operated spraying systems are well known.
Some systems have been described which cap a conventional paint can and tightly grip the paint can against the possibilities of explosions and pressure leaks and then deliver air from a compressor into the paint can to force paint out through an elongated tube to a roller for distribution. The clamps may be difficult to apply uniformly to insure against rupture or leakage of the pails, and an expensive air compressor is required to drive the paint.
An additional drawback of spraying devices is the need to initially and continuously adjust the paint viscosity to a correct degree for preventing clogging of the sprayer or running of the coating once it is applied.